Leaf springs are the long, flat springs under the rear end of a car or truck. They are designed to be a load-bearing spring more than a suspension spring. If the springs are bad, it is very easy for the average car owner to know. Unless you are a certified mechanic, it is not recommended that you attempt to replace them. They are also important if you are using a vehicle to tow. These springs will hold the load. If you are planning on towing something, it is advisable to have an extra leaf placed in the springs.
Park the car on a level surface. Placer the level on the roof of the car. Make sure that it is in the centre. If the car is out of level in the back of the vehicle, then the leaf springs may be bad. To test this, push down on the rear of the car. If it goes down easily, then the leaf springs may be bad. If it comes up slowly, the shocks are still good, so you will need to look deeper into the problem.
Look under the car at the leaf springs. If they are rusted and there are large chunks of the leaf springs missing, then you may want to have them replaced. The leaf springs will be the long stacked set of metal beams that run parallel to the to the car frame. If you see one of these beams broken, you will have to have them replaced.
Drive the car over a bumpy road. If the vehicle bounces or seems as if it is going to skid sideways, then the leaf springs are bad. They are causing the shocks to try to absorb too much punishment, and the shocks are designed for relieving these bumps, not taking the whole impact.
Attach a payload to the trailer hitch. If the vehicle is used for towing, the best way to see if it is the leaf springs is to see if the load is forcing the rear of the vehicle down. If this is the case, you are either towing too heavy a payload or the springs not good. If it has never sagged, then the leaf springs are bad.